Image scanning apparatuses such as image scanners, copiers, printers and multi function peripherals (MFPs) are widely used in daily lives or offices for scanning images of objects such as paper sheets. As known, the image scanning apparatus usually has an automatic document feeder for automatically and continuously feeding many paper sheets one by one. During operation of the automatic document feeder, the paper sheet is readily jammed. For example, the paper sheets that are too thick or too thin may cause jams. In addition, if the paper sheet is too wet or too dry such that the paper sheet may be softened or hardened, or if the smoothness or length of the paper sheet is improper, the paper sheet is transported across the feeding path with difficulty. Moreover, if the paper feeding operation is abruptly interrupted, the possibility of getting jammed paper sheet is increased. Conventionally, the automatic document feeder has a paper release mechanism for removing the jammed paper sheet.
Referring to FIG. 1, a schematic cross-sectional view of an automatic document feeder having a mechanism for releasing paper jam is illustrated. The automatic document feeder includes a first transfer roller assembly 100, a second transfer roller assembly 110 and a third transfer roller assembly 120. During operation of the automatic document feeder, the paper sheet is moved along the feeding path 130 and successively transported across the first transfer roller assembly 110, the second transfer roller assembly 110 and the third transfer roller assembly 120.
The first transfer roller assembly 100 and the second transfer roller assembly 110 are coupled to the upper cover 140 of the automatic document feeder. A first transfer follower roller 111 of the first transfer roller assembly 100 and a second transfer follower roller 121 of the second transfer roller assembly 110 are both coupled to the upper cover 140. In a case that the paper sheet is jammed in the vicinity of the first transfer roller assembly 100 or the second transfer roller assembly 110, the user may uplift the upper cover 140 in the direction as indicated by the arrow 150 to release the first transfer roller assembly 100 and the second transfer roller assembly 110 while easily pulling out the jammed paper.
In contrast, if the paper sheet is jammed in the vicinity of the third transfer roller assembly 120, the user needs to pull out the jammed paper in the direction as indicated by the arrow 160 or 170 by exerting a pulling force. Since the pulling force needs to be large enough to pull out the jammed paper, the paper sheet may be fractured or broken in the feeding path 130 of the automatic document feeder.
Please refer to FIG. 1 again. A transmission mechanism is arranged between the third transfer roller assembly 120 and a motor 180. The transmission mechanism includes a plurality of gears. These gears are engaged with each other. During the process of pulling out the paper sheet jammed in the third transfer roller assembly 120, the motor 180 may generate a damping-reinforced effect and thus the resistive force is increased. That is why the paper sheet jammed in the third transfer roller assembly 120 is pulled out with difficulty.
In views of the above-described disadvantages resulted from the prior art, the applicant keeps on carving unflaggingly to develop an automatic document feeder having a mechanism for releasing paper jam in order to minimize the damping-reinforced effect and facilitate easily releasing the jammed paper.